Validation of the Skin Symptom Assessment (SSA) questionnaire for the evaluation of radiation dermatitis in breast cancer patients.

PURPOSE: Radiation dermatitis (RD) is a painful side effect of radiation therapy (RT). The objective of this analysis was to investigate the validity and reliability of the Skin Symptom Assessment (SSA) questionnaire in evaluating the severity of patient- and clinician-reported outcomes for RD in breast cancer patients by comparing it to a validated assessment tool, the Radiation-Induced Skin Reaction Assessment Scale (RISRAS) questionnaire. METHODS: This study compared patient and clinician-reported outcomes for RD from previous clinical trials conducted in a Canadian cancer centre. The analysis included 376 and 38 patients in the two trials using Mepitel Film (doi.org/10.1200) and StrataXRT (clinicaltrials.gov identifier: NCT05594498), respectively. Patients in both studies completed the SSA and RISRAS questionnaires at baseline, 2-weeks post-RT, and 3 months after completion of RT. Clinician SSA and RISRAS assessments were collected at baseline and 2-weeks post-RT. These time points were analyzed longitudinally to investigate the SSA's validity in RD symptom assessment. RESULTS: The majority of patient-reported items on the SSA and RISRAS assessments demonstrated positive significant associations between symptoms of itchiness, between pain/soreness and pain/discomfort, and between blistering or erythema with burning sensation items. All items in the clinician-reported SSA and clinician component of RISRAS showed positive statistical significance between items measuring erythema, pigmentation or edema with dry desquamation, and blistering/peeling with moist desquamation. CONCLUSIONS: The SSA has been validated for assessing patient- and clinician-reported symptoms of RD accurately as outcomes correlate well with the previously validated RISRAS assessment.

StrataXRT for the prevention of acute radiation dermatitis in breast cancer: a pilot study.

PURPOSE: Previous literature has produced heterogeneous results on StrataXRT for prevention of acute radiation dermatitis (RD) in breast cancer. This pilot study aimed to assess the feasibility and efficacy of StrataXRT in a cancer center. METHODS: The study consisted of five cohorts: (1) patients with large breasts treated with local radiation therapy (RT) either in the supine position or (2) the prone position, (3) patients receiving locoregional breast RT with any breast size, and (4) patients receiving chest wall RT, either locally or (5) locoregionally. The primary endpoint of the study was RD grade as assessed using the Common Terminology Criteria for Adverse Events. Secondary endpoints included incidence of moist desquamation (MD), patient- and clinician-reported skin assessments, patient quality of life as assessed by the Skindex-16, and patient satisfaction. These outcomes were compared with those from a published trial from the same institution assessing standard of care and Mepitel Film (MF) as prevention of breast RD. RESULTS: Forty-five patients receiving RT to the breast or chest wall were enrolled. Two withdrew, leaving 43 evaluable patients. Overall, two (4.7%) patients had grade 3 RD, 14 (32.6%) had grade 2 RD, and 27 (62.8%) had grade 1 RD. Ten patients (23.3%) developed MD during/after RT. CONCLUSION: StrataXRT is effective in preventing grade 3 RD in patients, and the most promising results were observed within the prone cohort. Further research includes evaluating the efficacy of StrataXRT against the standard of care for the prophylaxis of RD. TRIAL REGISTRATION: The study protocol was registered at ClinicalTrials.gov (identifier: NCT05594498) on October 13, 2022.

Barrier films or dressings for the prevention of acute radiation dermatitis in breast cancer: a systematic review and network meta-analysis.

BACKGROUND: Barrier films or dressings were reported to be effective in preventing radiation dermatitis (RD) in breast cancer patients, but their comparative efficacy is unknown. METHODS: A systematic literature search was performed on Embase, MEDLINE and Cochrane CENTRAL Registry of Clinical Trials from inception to October 20, 2023. Randomised controlled trials (RCTs) comparing barrier films or dressings to the standard of care (SOC) or other interventions were included. We estimated summary odds ratios and mean differences using network meta-analysis with random effects. This study was registered with PROSPERO (ID: CRD42023475021). RESULTS: Fourteen RCTs met inclusion criteria. Six interventions were analysed: 3M™ Moisturizing Double Barrier Cream (MDBC), 3M™ No Sting Barrier Film (BF), Hydrofilm® (HF), Mepitel® Film (MF), Silver Leaf Nylon Dressing and StrataXRT®. HF, MF and StrataXRT® reduced the incidence of moist desquamation compared to SOC (HF: OR = 0.08; p = 0.02; MF: OR = 0.31 p < 0.01; StrataXRT®: OR = 0.22, p = 0.04). The ranking of agents from most to least effective in preventing moist desquamation according to P-scores was HF (92.5%), MF (78.5%), StrataXRT® (70.1%), BF (46.4%), Silver Leaf Nylon Dressing (24.9%), MDBC (22.9%) and SOC (14.7%). Only four RCTs on HF and MF included patient-reported outcome (PRO) assessments that allowed pooling for analysis. HF and MF were more effective in reducing pain, itchiness and burning sensation compared to SOC (p < 0.01 for all symptoms). CONCLUSION: HF and MF were effective in preventing RD in breast cancer. Future RCTs should compare these interventions to effective cream preparations, such as topical corticosteroids.

Utilizing radiomics and dosiomics with AI for precision prediction of radiation dermatitis in breast cancer patients.

PURPOSE: This study explores integrating clinical features with radiomic and dosiomic characteristics into AI models to enhance the prediction accuracy of radiation dermatitis (RD) in breast cancer patients undergoing volumetric modulated arc therapy (VMAT). MATERIALS AND METHODS: This study involved a retrospective analysis of 120 breast cancer patients treated with VMAT at Kaohsiung Veterans General Hospital from 2018 to 2023. Patient data included CT images, radiation doses, Dose-Volume Histogram (DVH) data, and clinical information. Using a Treatment Planning System (TPS), we segmented CT images into Regions of Interest (ROIs) to extract radiomic and dosiomic features, focusing on intensity, shape, texture, and dose distribution characteristics. Features significantly associated with the development of RD were identified using ANOVA and LASSO regression (p-value < 0.05). These features were then employed to train and evaluate Logistic Regression (LR) and Random Forest (RF) models, using tenfold cross-validation to ensure robust assessment of model efficacy. RESULTS: In this study, 102 out of 120 VMAT-treated breast cancer patients were included in the detailed analysis. Thirty-two percent of these patients developed Grade 2+ RD. Age and BMI were identified as significant clinical predictors. Through feature selection, we narrowed down the vast pool of radiomic and dosiomic data to 689 features, distributed across 10 feature subsets for model construction. In the LR model, the J subset, comprising DVH, Radiomics, and Dosiomics features, demonstrated the highest predictive performance with an AUC of 0.82. The RF model showed that subset I, which includes clinical, radiomic, and dosiomic features, achieved the best predictive accuracy with an AUC of 0.83. These results emphasize that integrating radiomic and dosiomic features significantly enhances the prediction of Grade 2+ RD. CONCLUSION: Integrating clinical, radiomic, and dosiomic characteristics into AI models significantly improves the prediction of Grade 2+ RD risk in breast cancer patients post-VMAT. The RF model analysis demonstrates that a comprehensive feature set maximizes predictive efficacy, marking a promising step towards utilizing AI in radiation therapy risk assessment and enhancing patient care outcomes.

Spray skin protectant versus standard moisturiser in the prevention of radiodermatitis in patients with anal canal and rectal cancer: A randomised clinical trial.

The evidence on products for the prevention of radiodermatitis is limited. The primary objective was to analyse the effectiveness of the spray skin protectant 'non-burning barrier film' in the prevention of radiodermatitis with moist desquamation in patients with the anal canal and rectal cancer followed in nursing consultations compared to a standardised moisturiser based on Calendula officinalis and Aloe barbadensis. Single-blind randomised clinical trial. The study was performed in a hospital in Rio de Janeiro, Brazil, with 63 patients undergoing anal canal and rectal cancer treatment, randomised into one of the following two groups: an experimental group, which used a spray skin protectant and a control group, which used a moisturiser. Data were collected using an initial and subsequent evaluation form and were assessed using descriptive and inferential analyses. Participants who used the spray skin protectant had a lower chance of presenting radiodermatitis with moist desquamation and a longer time without this outcome when compared to the control group. The overall incidence of radiodermatitis was 100%, with 36.5% being severe. Furthermore, 17.5% of participants discontinued radiotherapy due to radiodermatitis. There were no differences between the groups regarding the severity of radiodermatitis and the number of patients who discontinued radiotherapy. The skin protectant was effective in preventing radiodermatitis with moist desquamation amongst patients with anal canal and rectal cancer.

Radiation recall reaction induced by gemcitabine/docetaxel in children: A retrospective study on risk factors and outcomes.

INTRODUCTION: Radiation recall reaction (RRR) is a rare inflammatory reaction developing in a previously irradiated field after a triggering agent. In pediatric patients, it is poorly understood and deficiently studied. Gemcitabine-docetaxel (G/D) in childhood cancer is mainly used as a salvage regimen for sarcomas. We aim to describe RRR triggered by G/D in children. PATIENTS AND METHODS: Retrospective review of 21 patients receiving G/D along with radiotherapy at two hospitals from 2010 until 2022. RRR was considered as any toxicity occurring after G/D administration in a previously irradiated field. RRR features were described. Fisher's and Mann-Whitney tests were utilized to analyze the risk factors involved. RESULTS: Sixteen episodes of RRR developed in 16 (76.2%) patients. RRR mainly involved deep layers of the skin (58%) and occurred predominantly after two G/D cycles. The mean time between radiotherapy and chemotherapy was 28.5 days (0-1359 days), and the mean radiation volume 391 mL (157-1810 mL) for RRR. RRR treatment was mainly systemic steroids, with partial responses in six of 11 (58%) patients. Re-exposure to G/D was associated with a high rate of recurrence in nine of 15 (56.2%), prompting drug discontinuation. The major risk factors for RRR after G/D include, without statistical significance, a larger volume of the irradiated field and a shorter interval between chemotherapy and radiotherapy. CONCLUSIONS: The incidence of RRR after G/D in the pediatric population is higher than previously reported. Drug re-exposure is usually followed by recurrence. Higher irradiated volumes and a shorter time to the start of chemotherapy could be related with an increased risk of RRR.

Comparison of liposomal gel with and without addition of chamomile for prevention of radiation dermatitis in head and neck cancer patients: A randomized controlled trial.

BACKGROUND AND PURPOSE: Head and neck cancer patients frequently develop radiation dermatitis (RD) during radiotherapy. We compared liposomal gel with and without chamomile extract for the prevention and management of RD in head and neck cancer patients undergoing radiotherapy. MATERIALS AND METHODS: Sixty participants undergoing radiotherapy for the first time for head and neck cancer were recruited in a double-blind randomized clinical trial. Primary outcomes were the occurrence of dry desquamation and the cumulative dose of ionizing radiation at the first occurrence of dry desquamation. Secondary outcomes were the occurrence of erythema, moist desquamation, global RD, and participant self-reported symptoms. RESULTS: Dry desquamation occurred in 76.9 % (95 % CI: 57.9, 89.0) of participants in the chamomile liposomal gel group and in 88.9 % (95 % CI: 71.9, 96.1) in the liposomal gel group (p = 0.43). The median cumulative dose of ionizing radiation when dry desquamation occurred was 48.0 Gy in the chamomile liposomal gel group and 40.0 Gy in the liposomal gel group. Fewer symptoms were reported in the chamomile liposomal gel group. CONCLUSION: No statistically significant differences in outcomes were found between the two groups, though the chamomile liposomal gel group presented with lower grades of RD than the liposomal gel group. In addition, when compared to the literature on other topical interventions to manage RD, our results show that chamomile liposomal gel has potential for better management and prevention of RD in this population, which should be further tested. This study provides crucial information to design future studies. Clinical Trials Registration (REBEC): RBR-92cts3.

Feasibility and Safety of the "One-Week Breast Radiation Therapy" Program.

AIMS: FAST-Forward and UK-FAST-trials have demonstrated the safety and efficacy of five-fraction breast adjuvant radiation therapy (RT) and have become the standard of care for selected early breast cancer patients. In response to the additional burden caused by the COVID-19 pandemic, we implemented "One-Week Breast RT," an innovative program delivering five-fraction whole breast RT in a complete 5-day workflow. The primary objective of this study was to demonstrate the feasibility and safety of our program. The secondary objective was to evaluate cosmetic results. MATERIAL AND METHODS: A total of 120 patients treated from February 2021 to March 2022, received whole breast RT without lymph node irradiation nor boost, with 26 Gy in five fractions over one week. Inverse planning with restricted optimization parameters offers systematic deep inspiration breath-hold aimed to provide treatment plans compliant with FAST-Forward recommendations. Toxicity and cosmetic evaluations were prospectively registered prior (pre-RT), at the end (end-RT), and 6 months after RT (6 months) based on Common Terminology Criteria for Adverse Events v. 4.03 and Harvard scale. RESULTS: With a median age of 70 years (interquartile range (IQR): 66-74) and a median follow-up of 6 months (IQR: 6.01-6.25), most patients (93.3%) completed their RT in one week from baseline to the end of the treatment consultation. The most common acute toxicities (at end-RT) were skin-related: radio-dermatitis (72%), induration (35%), hyperpigmentation (8%), and breast edema (16%). The rate of radio-dermatitis decreased from end-RT to 6 months (71.7% vs 5.4%, P< 0.001). No patient experienced grade ≥3 toxicity. At 6 months, cosmetic results were generally good or excellent (94.1%). CONCLUSION: This study confirms the feasibility and acute safety of the "One-Week Breast RT" in real life. Favorable toxicity profiles and good cosmetic outcomes are in line with FAST-Forward results. A prospective national cohort, aimed at decreasing treatment burden, maintaining safety, efficacy, and improving RT workflow efficiency with longer follow-up is ongoing.

Acute radiation skin injury in stage III-IV head and neck cancer: scale correlates and predictive model.

PURPOSE: Active radiation skin injury (ARSI) has the highest incidence of acute adverse reactions caused by radiotherapy (RT) in patients with head and neck cancer (HNC). This study aimed to screen risk factors that can facilitate the identification of HNC patients at high risk of ARSI. METHODS: Data from 255 stage III-IV HNC patients who underwent intensity-modulated radiation therapy (IMRT) were collected. The data from our medical records, including clinical characteristics and hematological indices before RT, were retrospectively collected and arranged. The Common Terminology Criteria for Adverse Events Criteria (CTCAE), Radiation Therapy Oncology Group Criteria (RTOG), World Health Organization Criteria (WHO), Oncology Nursing Society (ONS), Acute Radiation Dermatitis Graduation Scale, Douglas & Fowler and Radiation Dermatitis Severity Scale (RDSS) were used to assess ARSI. Of these, CTCAE was used for further analysis. Binary logistic regression analyses were used to identity risk factors. To establish the correction between each risk factor and the ARSI score, the odds ratio (OR) and 95% confidence interval (CI) were computed. RESULTS: The assessment results of the CTCAE with RTOG, WHO, ONS, Graduation Scale, Douglas & Fowler and RDSS have good consistency. After radiotherapy, 18.4% of patients had at least 3 (3 +) grade ARSI. Multivariate logistic regression analysis revealed that the KPS score, blood glucose level, white blood cell count, and plasma free thyroxine (FT4) concentration were independent risk factors for 3 + grade ARSI. A nomogram was constructed on the basis of these risk factors, which demonstrated good predictive power according to the area under the ROC curve (AUC). The satisfactory consistency and clinical efficacy of the nomogram were confirmed by calibration curves and decision curve analysis (DCA). CONCLUSION: A low KPS score, high blood glucose level, high white blood cell count, and high thyroid hormone prior to radiotherapy for stage III-IV HNC are independent risk factors for grade 3 + RSI.

Development of a risk prediction model for radiation dermatitis following proton radiotherapy in head and neck cancer using ensemble machine learning.

PURPOSE: This study aims to develop an ensemble machine learning-based (EML-based) risk prediction model for radiation dermatitis (RD) in patients with head and neck cancer undergoing proton radiotherapy, with the goal of achieving superior predictive performance compared to traditional models. MATERIALS AND METHODS: Data from 57 head and neck cancer patients treated with intensity-modulated proton therapy at Kaohsiung Chang Gung Memorial Hospital were analyzed. The study incorporated 11 clinical and 9 dosimetric parameters. Pearson's correlation was used to eliminate highly correlated variables, followed by feature selection via LASSO to focus on potential RD predictors. Model training involved traditional logistic regression (LR) and advanced ensemble methods such as Random Forest and XGBoost, which were optimized through hyperparameter tuning. RESULTS: Feature selection identified six key predictors, including smoking history and specific dosimetric parameters. Ensemble machine learning models, particularly XGBoost, demonstrated superior performance, achieving the highest AUC of 0.890. Feature importance was assessed using SHAP (SHapley Additive exPlanations) values, which underscored the relevance of various clinical and dosimetric factors in predicting RD. CONCLUSION: The study confirms that EML methods, especially XGBoost with its boosting algorithm, provide superior predictive accuracy, enhanced feature selection, and improved data handling compared to traditional LR. While LR offers greater interpretability, the precision and broader applicability of EML make it more suitable for complex medical prediction tasks, such as predicting radiation dermatitis. Given these advantages, EML is highly recommended for further research and application in clinical settings.

Acute skin toxicity and self-management ability among Chinese breast cancer radiotherapy patients: a qualitative study.

OBJECTIVES: Radiation dermatitis is the most common reaction to radiotherapy, almost all breast cancer patients receive radiotherapy on an outpatient basis. Currently, there are no studies on the experience of radiation dermatitis and the ability to self-manage it. Therefore, we aimed to use qualitative approaches to gain a deeper understanding of the actual experiences and self-management ability in order to provide a reference for further improving the effectiveness of self-management and to optimize symptom management strategies. METHODS: A descriptive qualitative study was conducted using purposive sampling to select 17 breast cancer patients undergoing radiotherapy. Semi-structured interviews were conducted from September to November 2023. The Colaizzi seven-step analysis method was used to classify the data into summarized themes. RESULTS: Four themes were identified from the interview responses: (1) multiple self-reported skin symptoms in breast cancer patients with radiation dermatitis; (2) the multidimensional impact on patient's quality of life, especially pruritus, ulceration; (3) the ability to self-manage radiation dermatitis: strong mental toughness, positive response, and self-doubt; (4) challenges faced: concerns about radiotherapy side effects and recurrence, targeted symptom management and continuity of care after the radiotherapy. CONCLUSIONS: Healthcare professionals should consider patients' self-reported symptoms when assessing radiation dermatitis. For pruritus and pain, we can enhance precision symptom management to improve patients' quality of life. By utilizing information technology tools, we can increase breast cancer patients' ability and confidence in managing radiation dermatitis effectively while enhancing accurate symptom management during radiotherapy.

Seasonal Impact on Grade ≥2 Dermatitis in Patients With Breast Cancer Undergoing Radiotherapy: A Supplementary Analysis.

BACKGROUND/AIM: We investigated grade ≥2 dermatitis in patients irradiated for breast cancer. This study evaluated associations between dermatitis and the season during which radiotherapy took place. PATIENTS AND METHODS: Associations between the season and grade ≥2 dermatitis were retrospectively evaluated in 327 breast cancer patients. Seasons were March to May (spring), June to August (summer), September to November (autumn), and December to February (winter). Subgroup analyses were performed considering fractionation, radiation technique, treatment volume, radiation boost, and deep-inspiration breath-hold technique. Furthermore, warmer and cooler months were compared. RESULTS: The season had no significant impact on the rate of grade ≥2 dermatitis in the entire cohort (p=0.63) nor in the subgroup analyses (p-values between 0.17 and 0.82). No significant difference in rate was found between warm and cool months. CONCLUSION: Grade ≥2 dermatitis was not associated with the season during which radiotherapy was performed. This factor may not be important for stratification in prospective trials.

Dose-toxicity surface histogram-based prediction of radiation dermatitis severity and shape.

Objective.This study aimed to develop a new approach to predict radiation dermatitis (RD) by using the skin dose distribution in the actual area of RD occurrence to determine the predictive dose by grade.Approach.Twenty-three patients with head and neck cancer treated with volumetric modulated arc therapy were prospectively and retrospectively enrolled. A framework was developed to segment the RD occurrence area in skin photography by matching the skin surface image obtained using a 3D camera with the skin dose distribution. RD predictive doses were generated using the dose-toxicity surface histogram (DTH) calculated from the skin dose distribution within the segmented RD regions classified by severity. We then evaluated whether the developed DTH-based framework could visually predict RD grades and their occurrence areas and shapes according to severity.Main results.The developed framework successfully generated the DTH for three different RD severities: faint erythema (grade 1), dry desquamation (grade 2), and moist desquamation (grade 3); 48 DTHs were obtained from 23 patients: 23, 22, and 3 DTHs for grades 1, 2, and 3, respectively. The RD predictive doses determined using DTHs were 28.9 Gy, 38.1 Gy, and 54.3 Gy for grades 1, 2, and 3, respectively. The estimated RD occurrence area visualized by the DTH-based RD predictive dose showed acceptable agreement for all grades compared with the actual RD region in the patient. The predicted RD grade was accurate, except in two patients.Significance. The developed DTH-based framework can classify and determine RD predictive doses according to severity and visually predict the occurrence area and shape of different RD severities. The proposed approach can be used to predict the severity and shape of potential RD in patients and thus aid physicians in decision making.

Risk Prediction Model for Radiation-induced Dermatitis in Patients with Cervical Carcinoma Undergoing Chemoradiotherapy.

PURPOSE: Radiation-induced dermatitis (RD) is a common side-effect of therapeutic ionizing radiation that can severely affect patient quality of life. This study aimed to develop a risk prediction model for the occurrence of RD in patients with cervical carcinoma undergoing chemoradiotherapy using electronic medical records (EMRs). METHODS: Using EMRs, the clinical data of patients who underwent simultaneous radiotherapy and chemotherapy at a tertiary cancer hospital between 2017 and 2022 were retrospectively collected, and the patients were divided into two groups: a training group and a validation group. A predictive model was constructed to predict the development of RD in patients who underwent concurrent radiotherapy and chemotherapy for cervical cancer. Finally, the model's efficacy was validated using a receiver operating characteristic curve. RESULTS: The incidence of radiation dermatitis was 89.5% (560/626) in the entire cohort, 88.6% (388/438) in the training group, and 91.5% (172/188) in the experimental group. The nomogram was established based on the following factors: age, the days between the beginning and conclusion of radiotherapy, the serum albumin after chemoradiotherapy, the use of single or multiple drugs for concurrent chemotherapy, and the total dose of afterloading radiotherapy. Internal and external verification indicated that the model had good discriminatory ability. Overall, the model achieved an area under the receiver operating characteristic curve of .66. CONCLUSIONS: The risk of RD in patients with cervical carcinoma undergoing chemoradiotherapy is high. A risk prediction model can be developed for RD in cervical carcinoma patients undergoing chemoradiotherapy, based on over 5 years of EMR data from a tertiary cancer hospital.

Evolution of radiation-induced dermatitis treatment.

Radiation-induced skin damage (RID) is the most prevalent, significant side effect of radiotherapy (RT). Nearly 95% of patients experience moderate to severe skin reactions after receiving radiation therapy. However, criteria for acute radiation dermatitis (ARD) treatment remain unavailable. Topical agents with anti-inflammatory properties may protect the skin and facilitate tissue regeneration in patients with RID. Many of these topical agents function through nuclear factor kappa B pathway regulation. They either reduce the levels of inflammatory factors or elicit anti-inflammatory properties of their own, thus preventing oxidative stress and inflammatory responses and thus enabling RID prevention and management. Herein, we explore the 25 topical agents investigated for RID prevention and management thus far and evaluate their mechanisms of action. These agents include 11 natural agents, 3 miscellaneous agents, 9 topical nonsteroidal agents, and 2 topical corticosteroids.

Computational Model Based on Optical Coherence Tomography (OCT) Skin Scanning to Identify and Quantify Acute Radiation Dermatitis (ARD): A Prospective Diagnostic Study.

BACKGROUND: Acute radiation dermatitis (ARD) is the most widely reported radiotherapy-induced adverse event. Currently, there is no objective or reliable method to measure ARD. OBJECTIVE: Our main objective was to identify and quantify the effects of radiotherapy with a computational model using optical coherence tomography (OCT) skin scanning. Secondary objectives included determining the ARD impact of different radiotherapeutic schemes and adjuvant topical therapies. METHODS: We conducted a prospective, single-center case series study in a tertiary referral center of patients with breast cancer who were eligible for whole breast radiotherapy (WBRT). RESULTS: A total of 39 women were included and distributed according to the radiotherapeutic schemes (15, 20, and 25 fractions). A computational model was designed to quantitatively analyze OCT findings. After radiotherapy, OCT scanning was more sensitive revealing vascularization changes in 84.6% of the patients (vs 69.2% of the patients with ARD by clinical examination). OCT quantified an increased vascularization at the end of WBRT (P<.05) and a decrease after 3 months (P=.032). Erythematous skin changes by OCT were more pronounced in the 25-fraction regime. CONCLUSION: An OCT computational model allowed for the identification and quantification of vascularization changes on irradiated skin, even in the absence of clinical ARD. This may allow the design of standardized protocols for ARD beyond the skin color of the patients involved.

Oxygen Enhancement Ratio-Weighted Dose Quantitatively Describes Acute Skin Toxicity Variations in Mice After Pencil Beam Scanning Proton FLASH Irradiation With Changing Doses and Time Structures.

PURPOSE: The aim of this work was to investigate the ability of a biological oxygen enhancement ratio-weighted dose, DOER, to describe acute skin toxicity variations observed in mice after proton pencil beam scanning irradiations with changing doses and beam time structures. METHODS AND MATERIALS: In five independent experiments, the right hind leg of a total of 621 CDF1 mice was irradiated previously in the entrance plateau of a pencil beam scanning proton beam. The incidence of acute skin toxicity (of level 1.5-2.0-2.5-3.0-3.5) was scored for 47 different mouse groups that mapped toxicity as function of dose for conventional and FLASH dose rate, toxicity as function of field dose rate with and without repainting, and toxicity when splitting the treatment into 1 to 6 identical deliveries separated by 2 minutes. DOER was calculated for all mouse groups using a simple oxygen kinetics model to describe oxygen depletion. The three independent model parameters (oxygen-depletion rate, oxygen-recovery rate, oxygen level without irradiation) were fitted to the experimental data. The ability of DOER to describe the toxicity variations across all experiments was investigated by comparing DOER-response curves across the five independent experiments. RESULTS: After conversion from the independent variable tested in each experiment to DOER, all five experiments had similar MDDOER50 (DOER giving 50% toxicity incidence) with standard deviations of 0.45 - 1.6 Gy for the five toxicity levels. DOER could thus describe the observed toxicity variations across all experiments. CONCLUSIONS: DOER described the varying FLASH-sparing effect observed for a wide range of conditions. Calculation of DOER for other irradiation conditions can quantitatively estimate the FLASH-sparing effect for arbitrary irradiations for the investigated murine model. With appropriate fitting parameters DOER also may be able to describe FLASH effect variations with dose and dose rate for other assays and endpoints.